Phenazopyridine compounds

ABSTRACT

The present invention is directed to substituted phenazopyridines represented by Formula I. The present invention also relates to the discovery that compounds of Formula I have increased bioavailability as compared to unconjugated phenazopyridine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention describes phenazopyridine covalently attached to variousconjugates. These compounds and compositions are useful for providingincreased (oral) bioavailability with reduced side effects.

2. Related Art

Various publications are cited herein, the disclosures of which areincorporated by reference in their entireties. However, the citation ofany reference herein should not be construed as an admission that suchreference is available as prior art to the present application.

Phenazopyridine is an analgesic compound indicated for urinary tractpain, burning, irritation, and discomfort, as well as urgent andfrequent urination caused by urinary tract infections, surgery, injury,or examination procedures. Phenazopyridine, while an effectiveanalgesic, carries with it a foreboding side effect profile, withnausea, vomiting, and general GI upset being the most severe events. Inan effort to improve the side effect profile and expand the use ofphenazopyridine, it is proposed to pursue the development of a prodrugcompound that results in the formation of the active drug followingtransport across the gastrointestinal epithelium.

Phenazopyridine or 2,6-pyridinediamine, 3-(phenylazo), monochloride (CASnumber 94-78-0) is an azo dye that exerts topical analgesic or localanesthetic action on the urinary tract mucosa and provides symptomaticrelief of pain, burning, urgency, frequency and other discomfortsarising from irritation of lower urinary tract caused by infections,trauma, surgery, endoscopic procedures or use of catheters.Phenazopyridine has been marketed since 1925 and since 1951 has had adual status of prescription and over-the-counter (OTC).

Phenazopyridine is marketed as single agent 100 and 200 mg tablets undera number of brand names including Nefrecil, Phenazodine, Pyridiate,Pyridium, Sedural, Uricalm, Uropyrine, Urodine, and Urogesic. Singleagent OTC medications include Azo-Gesic, Azo-Standard, and Uristat (95mg tablets), ReAzo (97 mg tablets), and URIRelief and Baridium (97.2 mgtablets). Phenazopyridine is available as a combined prescription withsulfisoxazole or sulfamethoxazole/trimethoprim and as Phenazopyridineplus in combination with hyosciamine and secbarbitol.

The usual adult dosage is 100-200 mg three times daily after meals forno more than two days and 12 mg/kg/day in three divided doses aftermeals in children for no more than two days. The pharmacologicalmechanism of the analgesic effect of phenazopyridine is unknown.

Phenazopyridine is absorbed from the gastrointestinal tract followingoral administration. Although the absolute bioavailability in humans hasnot been determined it is apparently poorly absorbed with the highestprescribed dose of 200 mg yielding maximum plasma levels between 10 and20 ng/mL. Phenazopyridine is rapidly excreted up to 65% unchanged inurine with approximately 90% of a single dose cleared within 24 hours.Metabolites include aniline, N-acetyl-p-aminophenol (NAPA oracetaminophen) and p-amino phenol. Aniline may contribute to theanalgesic effect of orally administered phenazopyridine in the urinarytract mucosa.

Adverse reactions associated with therapeutic doses of phenazopyridineinclude headache, rash pruritus, gastrointestinal disturbances (nausea,vomiting, and diarrhea), orange to red urine discoloration and stainingof soft contact lenses. In cases of insufficient renal clearancephenazopyridine can tinge skin, sclera or fluids yellow due toaccumulation of the drug. Methemaglobenemia, hemolytic anemia, renal andhepatic toxicity have been reported, usually at overdose levels.Anaphylactoid reactions have been reported.

Phenazopyridine and the metabolite aniline can cause oxidative stresswithin red blood cells by conversion of hemoglobin to methemaglobin.Patients with glucose-6-phosphate dehydrogenase deficiency may bepredisposed to hemolytic anemia. Phenazopyridine should not beadministered to patients with impaired renal function. Exceeding therecommended dose may lead to increased serum levels and toxic reactions.Methemaglobinemia generally follows excessive acute overdose.Considering the long history and fairly widespread use ofphenazopyridine, reports of serious toxicity are relatively uncommon.

Long term (2 years) administration of phenazopyridine hydrochlorideinduced adenomas and adenocarcinomas in the large intestine of rats andlifetime administration caused hepatocellular adenomas and carcinomas infemale mice. Phenazopyridine has been shown to be mutagenic in bacteriaand mutagenic and clastogenic in mammalian cells. In one limitedepidemiological study of 2,214 patients who received phenazopyridinehydrochloride there was no observed increase in the occurrence of anytype of cancer over a minimum period of 3 years. Current phenazopyridineproduct labeling indicates: “Long term administration of phenazopyridinehydrochloride has induced neoplasia in rats (large intestine) and mice(liver). Although no association between phenazopyridine hydrochlorideand human neoplasia has been reported, adequate epidemiological studiesalong these lines have not been conducted.”

Reproduction studies at doses up to 50 mg/kg/day or 110 mg/kg/day inrats and 39 mg/kg/day in rabbits showed no effects on fertility orembryo-fetal development. Phenazopyridine is currently classified inpregnancy category B. There have been no adequate and well controlledstudies of phenazopyridine exposure in pregnant women. Surveillancestudies have been reported with no link of phenazopyridine use tocongenital defects. The Collaborative Perinatal Project monitored 50,282mother-child pairs with 1,109 exposures recorded during pregnancy and219 exposures during the first trimester. No association was found withmajor or minor malformations or individual defects. Surveillance of229,101 Michigan Medicaid patents identified 469 phenazopyridineexposures during the first trimester. No data was obtained to indicateany association of the drug with abnormalities.

The acute toxicity LD50 for phenazopyridine has been reported as 472mg/kg (oral) and 200 (i.p.) in rats; and 180 mg/kg (i.p.) in mice.Adequate safety pharmacology and repeat dose nonclinical toxicologystudies have not been performed for phenazopyridine.

BRIEF SUMMARY OF THE INVENTION

The invention provides covalent attachment of phenazopyridine andderivatives or analogs thereof to a variety of chemical moieties. Thechemical moieties may include any substance which results in a prodrugform, i.e., a molecule which is converted into its active form in thebody by normal metabolic processes. For example, the chemical moietiesmay be single amino acids, dipeptides, or polypeptides.

The chemical moiety is covalently attached either directly or indirectlythrough a linker to the phenazopyridine. The site of attachment istypically determined by the functional group(s) available on thephenazopyridine.

In one embodiment, the phenazopyridine is attached to a single aminoacid which is either naturally occurring or a synthetic amino acid. Inanother embodiment, the phenazopyridine is attached to a dipeptide ortripeptide, which could be any combination of the naturally occurringamino acids and synthetic amino acids. In another embodiment, the aminoacids are selected from L-amino acids for digestion by proteases.

Other objects, advantages and embodiments of the invention are describedbelow and will be obvious from this description and practice of theinvention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the plasma concentrations of variousphenazopyridine-amino acid conjugates in rats following oraladministration of the phenazopyridine conjugates. Phenazopyridine (PAP)plasma concentrations versus time profiles are shown followingadministration of PAP.HCl, Gly-PAP, alanyl-PAP, methionyl-PAP,histidinyl-PAP, tryptophanyl-PAP, valyl-PAP, and lysyl-PAP.

FIG. 2 is a depiction of 2-amino-6-aminoacetamido-3-E-phenazopyridinedihydrochloride.

FIG. 3 is a graph showing mean rat (male) plasma concentration curvesof 1) phenazopyridine from phenazopyridine hydrochloride (2.8 mg/kgcontaining 2.5 mg/kg phenazopyridine base), 2) phenazopyridine fromGly-PAP (4 mg/kg, containing 2.5 mg/kg phenazopyridine base), and 3)Gly-PAP intact prodrug from Gly-PAP (4 mg/kg, containing 2.5 mg/kgphenazopyridine base).

FIG. 4 is a graph showing mean rat (male) plasma concentration curvesof 1) phenazopyridine from phenazopyridine hydrochloride (2.8 mg/kgcontaining 2.5 mg/kg phenazopyridine base) and 2) phenazopyridine fromGly-PAP (0.9 mg/kg, containing 0.6 mg/kg phenazopyridine base).

FIG. 5 is a table showing the solubility of Gly-PAP at room temperatureas a free base and HCl salt.

FIG. 6 is a table showing the solubility of Gly-PAP salts in water andbioavailability in rats.

FIG. 7 is a table showing the results of a stability study of Gly-PAP byUV-HPLC.

FIG. 8 is a table showing the results of a stability study ofGly-PAP-HCl in water solution at 4° C. by UV-HPLC at 0.2 mg/ml.

FIG. 9 is a table showing the results of a stability study ofGly-PAP-HCl in water solution at 4° C. by UV-HPLC at 8.8 mg/ml.

FIG. 10 is a table showing the results of a stability study ofGly-PAP-HCL in water solution at room temperature by UV-HPLC.

FIG. 11 is a table summary of phenazopyridine pharmacokinetics followingoral administration of Gly-PAP or phenazopyridine HCl in male rats.

FIG. 12 is a table summary of Gly-PAP pharmacokinetics following oraladministration of Gly-PAP in male rats.

FIG. 13 is a graph showing mean dog (male) plasma concentration curvesof 2) phenazopyridine from phenazopyridine hydrochloride (5.9 mg/kgcontaining 5 mg/kg phenazopyridine base), 2) phenazopyridine fromGly-PAP (8.1 mg/kg, containing 5 mg/kg phenazopyridine base), and 3)Gly-PAP intact prodrug from Gly-PAP (8.1 mg/kg, containing 5 mg/kgphenazopyridine base).

FIG. 14 is a table summary of pharmacokinetic parameters in plasmacollected from male dogs following a single oral administration ofGly-PAP (Group 1) or PAP HCl (Group 2).

FIG. 15 is a table summary of concentrations of PAP and Gly-PAP in urinefollowing a single oral dose of Gly-PAP (Group 1) or PAP HCl (Group 2)to male dogs.

FIG. 16 is a synthetic scheme for production of2-amino-6-aminoacetamido-3-E-phenazopyridine dihydrochloride.

FIG. 17 is a table demonstrating oral bioavailability of Gly-PAP saltsin rats.

FIG. 18 is a table demonstrating reduction of the GI side effect ofemesis.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this application the use of “peptide” is meant to include asingle amino acid, a dipeptide, a tripeptide, an oligopeptide, apolypeptide, or the carrier peptide. Oligopeptide is meant to includefrom 2 amino acids to 70 amino acids. Further, at times the invention isdescribed as being an active agent attached to an amino acid, adipeptide, a tripeptide, an oligopeptide, polypeptide or carrier peptideto illustrate specific embodiments for the active agent conjugate.Preferred lengths of the conjugates and other preferred embodiments aredescribed herein.

A “composition” as used herein refers broadly to any compositioncontaining a described molecule conjugate(s). The composition maycomprise a dry formulation, an aqueous solution, or a sterilecomposition. Compositions comprising the molecules described herein maybe stored in freeze-dried form and may be associated with a stabilizingagent such as a carbohydrate. In use, the composition may be deployed inan aqueous solution containing salts, e.g., NaCl, detergents, e.g.,sodium dodecyl sulfate (SDS), and other components.

“Phenazopyridine” shall mean:

Compounds useful in the present invention are represented by Formula I:

wherein,R₁ and R₂ are independently

-   -   (a) hydrogen;    -   (b) the residue of an amino acid or peptide;    -   (c)

wherein R₃ is an optionally substituted alkyl or arylalkyl; or

-   -   (d) the residue of an amino acid wherein the amine of the amino        acid is protected with a t-butylcarbonyl;        wherein at least one of R₁ and R₂ is other than hydrogen.

This patent is meant to cover all compounds discussed regardless ofabsolute configurations. Thus, natural, L-amino acids are discussed butthe use of D-amino acids are also included.

Use of the phrases such as, “decreased”, “reduced”, “diminished” or“lowered” is meant to include at least a 10% change in side effects withgreater percentage changes being preferred. For instance, the change mayalso be greater than 25%, 35%, 45%, 55%, 65%, 75%, 85%, 95%, 96%, 97%,98%, 99%, or increments therein.

The purity of the prodrug will preferably be greater than 25%, 35%, 45%,55%, 65%, 75%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or increments therein.

The term increments is shall include without limitation, ones, tens, andfractions thereof, for instance, 1, 2, 3, 4, . . . or 0.1, 0.2, 0.3, 0.4etc.

For each of the recited embodiments, the amino acid or peptide maycomprise one or more of glycine or of the naturally occurring (L-) aminoacids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamicacid, glutamine, histidine, isoleucine, leucine, lysine, methionine,proline, phenylalanine, serine, tryptophan, threonine, tyrosine, andvaline. In another embodiment, the amino acid or peptide is comprised ofone or more of glycine or of the naturally occurring (D) amino acids:alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid,glutamine, histidine, isoleucine, leucine, lysine, methionine, proline,phenylalanine, serine, tryptophan, threonine, tyrosine, and valine. Inanother embodiment, the amino acid or peptide is comprised of one ormore unnatural, non-standard or synthetic amino acids such as,aminohexanoic acid, biphenylalanine, cyclohexylalanine,cyclohexylglycine, diethylglycine, dipropylglycine, 2,3-diaminopropionicacid, homophenylalanine, homoserine, homotyrosine, naphthylalanine,norleucine, ornithine, (4-fluoro)phenylalanine, (2,3,4,5,6pentafluoro)phenylalanine, (4-nitro)phenylalanine, phenylglycine,pipecolic acid, sarcosine, tetrahydroisoquinoline-3-carboxylic acid, andtert.-leucine. In another embodiment, the amino acid or peptidecomprises one or more amino acid alcohols, for example, serine andthreonine. In another embodiment the amino acid or peptide comprises oneor more N-methyl amino acids, for example, N-methylaspartic acid. Inanother embodiment, the amino acid or peptide comprises one or morecyclic amino acids, for example, cis-4-hydroxy-D-proline.

In another embodiment, the specific carriers are utilized as a baseshort chain amino acid sequence and additional amino acids are added tothe terminus or side chain. In another embodiment, the above amino acidsequence may have one more of the amino acids substituted with one ofthe 20 naturally occurring amino acids. It is preferred that thesubstitution be with an amino acid which is similar in structure orcharge compared to the amino acid in the sequence. For instance,isoleucine (Ile)[I] is structurally very similar to leucine (Leu)[L],whereas, tyrosine (Tyr)[Y] is similar to phenylalanine (Phe)[F], whereasserine (Ser)[S] is similar to threonine (Thr)[T], whereas cysteine(Cys)[C] is similar to methionine (Met)[M], whereas alanine (Ala)[A] issimilar to valine (Val)[V], whereas lysine (Lys)[K] is similar toarginine (Arg)[R], whereas asparagine (Asn)[N] is similar to glutamine(Gln)[Q], whereas aspartic acid (Asp)[D] is similar to glutamic acid(Glu)[E]. In the alternative, the preferred amino acid substitutions maybe selected according to hydrophilic properties (i.e., polarity) orother common characteristics associated with the 20 essential aminoacids. While preferred embodiments utilize the 20 natural amino acidsfor their GRAS characteristics, it is recognized that minorsubstitutions along the amino acid chain which do not affect theessential characteristics of the amino acid chain are also contemplated.

In one embodiment, the carrier range is between one to 12 chemicalmoieties with one to 8 moieties being preferred. In another embodiment,the number of chemical moieties is selected from 1, 2, 3, 4, 5, 6, or 7.

Formulations of the invention suitable for oral administration can bepresented as discrete units, such as capsules, caplets or tablets. Theseoral formulations also can comprise a solution or a suspension in anaqueous liquid or a non-aqueous liquid. The formulation can be anemulsion, such as an oil-in-water liquid emulsion or a water-in-oilliquid emulsion. The oils can be administered by adding the purified andsterilized liquids to a prepared enteral formula, which is then placedin the feeding tube of a patient who is unable to swallow.

Soft gel or soft gelatin capsules may be prepared, for example bydispersing the formulation in an appropriate vehicle (vegetable oils arecommonly used) to form a high viscosity mixture. This mixture is thenencapsulated with a gelatin based film using technology and machineryknown to those in the soft gel industry. The industrial units so formedare then dried to constant weight.

Chewable tablets, for example may be prepared by mixing the formulationswith excipients designed to form a relatively soft, flavored, tabletdosage form that is intended to be chewed rather than swallowed.Conventional tablet machinery and procedures, that is both directcompression and granulation, i.e., or slugging, before compression, canbe utilized. Those individuals involved in pharmaceutical solid dosageform production are versed in the processes and the machinery used asthe chewable dosage form is a very common dosage form in thepharmaceutical industry.

Film-coated tablets, for example may be prepared by coating tabletsusing techniques such as rotating pan coating methods or air suspensionmethods to deposit a contiguous film layer on a tablet.

Compressed tablets, for example may be prepared by mixing theformulation with excipients intended to add binding qualities todisintegration qualities. The mixture is either directly compressed orgranulated then compressed using methods and machinery known to those inthe industry. The resultant compressed tablet dosage units are thenpackaged according to market need, i.e., unit dose, rolls, bulk bottles,blister packs, etc.

The invention also contemplates the use of biologically-acceptablecarriers which may be prepared from a wide range of materials. Withoutbeing limited thereto, such materials include diluents, binders andadhesives, lubricants, plasticizers, disintegrants, colorants, bulkingsubstances, flavorings, sweeteners and miscellaneous materials such asbuffers and adsorbents in order to prepare a particular medicatedcomposition.

Binders may be selected from a wide range of materials such ashydroxypropylmethylcellulose, ethylcellulose, or other suitablecellulose derivatives, povidone, acrylic and methacrylic acidco-polymers, pharmaceutical glaze, gums, milk derivatives, such as whey,starches, and derivatives, as well as other conventional binders knownto persons skilled in the art. Exemplary non-limiting solvents arewater, ethanol, isopropyl alcohol, methylene chloride or mixtures andcombinations thereof. Exemplary non-limiting bulking substances includesugar, lactose, gelatin, starch, and silicon dioxide.

Preferred plasticizers may be selected from the group consisting ofdiethyl phthalate, diethyl sebacate, triethyl citrate, cronotic acid,propylene glycol, butyl phthalate, dibutyl sebacate, castor oil andmixtures thereof, without limitation. As is evident, the plasticizersmay be hydrophobic as well as hydrophilic in nature. Water-insolublehydrophobic substances, such as diethyl phthalate, diethyl sebacate andcastor oil are used to delay the release of water-soluble vitamins, suchas vitamin B6 and vitamin C. In contrast, hydrophilic plasticizers areused when water-insoluble vitamins are employed which aid in dissolvingthe encapsulated film, making channels in the surface, which aid innutritional composition release.

It should be understood that in addition to the ingredients particularlymentioned above, the formulations of this invention can include othersuitable agents such as flavoring agents, preservatives andantioxidants. Such antioxidants would be food acceptable and couldinclude vitamin E, carotene, BHT or other antioxidants known to those ofskill in the art.

Other compounds which may be included by admixture are, for example,medically inert ingredients, e.g., solid and liquid diluent, such aslactose, dextrose, saccharose, cellulose, starch or calcium phosphatefor tablets or capsules, olive oil or ethyl oleate for soft capsules andwater or vegetable oil for suspensions or emulsions; lubricating agentssuch as silica, talc, stearic acid, magnesium or calcium stearate and/orpolyethylene glycols; gelling agents such as colloidal clays; thickeningagents such as gum tragacanth or sodium alginate, binding agents such asstarches, arabic gums, gelatin, methylcellulose, carboxymethylcelluloseor polyvinylpyrrolidone; disintegrating agents such as starch, alginicacid, alginates or sodium starch glycolate; effervescing mixtures;dyestuff; sweeteners; wetting agents such as lecithin, polysorbates orlauryl sulfates; and other therapeutically acceptable accessoryingredients, such as humectants, preservatives, buffers andantioxidants, which are known additives for such formulations.

For oral administration, fine powders or granules containing diluting,dispersing and/or surface-active agents may be presented in a draught,in water or a syrup, in capsules or sachets in the dry state, in anon-aqueous suspension wherein suspending agents may be included, or ina suspension in water or a syrup. Where desirable or necessary,flavoring, preserving, suspending, thickening or emulsifying agents canbe included.

Liquid dispersions for oral administration may be syrups, emulsions orsuspensions. The syrups may contain as carrier, for example, saccharoseor saccharose with glycerol and/or mannitol and/or sorbitol. Thesuspensions and the emulsions may contain a carrier, for example anatural gum, agar, sodium alginate, pectin, methylcellulose,carboxymethylcellulose or polyvinyl alcohol.

The dose range for adult human beings will depend on a number of factorsincluding the age, weight and condition of the patient. Tablets andother forms of presentation provided in discrete units convenientlycontain a daily dose, or an appropriate fraction thereof, of one or moreof the compounds of the invention. For example, units may contain from 5mg to 500 mg, but more usually from 10 mg to 250 mg, of one or more ofthe compounds of the invention.

It is also possible for the dosage form to combine any forms of releaseknown to persons of ordinary skill in the art. These include immediaterelease, extended release, pulse release, variable release, controlledrelease, timed release, sustained release, delayed release, long acting,and combinations thereof. The ability to obtain immediate release,extended release, pulse release, variable release, controlled release,timed release, sustained release, delayed release, long actingcharacteristics and combinations thereof is known in the art.

Compositions of the invention may be administered in a partial, i.e.,fractional dose, one or more times during a 24 hour period, a singledose during a 24 hour period of time, a double dose during a 24 hourperiod of time, or more than a double dose during a 24 hour period oftime. Fractional, double or other multiple doses may be takensimultaneously or at different times during the 24 hour period. Thedoses may be uneven doses with regard to one another or with regard tothe individual components at different administration times.

Likewise, the compositions of the invention may be provided in a blisterpack or other such pharmaceutical package. Further, the compositions ofthe present inventive subject matter may further include or beaccompanied by indicia allowing individuals to identify the compositionsas products for a prescribed treatment. The indicia may additionallyinclude an indication of the above specified time periods foradministering the compositions. For example, the indicia may be timeindicia indicating a specific or general time of day for administrationof the composition, or the indicia may be a day indicia indicating a dayof the week for administration of the composition. The blister pack orother combination package may also include a second pharmaceuticalproduct.

It will be appreciated that the pharmacological activity of thecompositions of the invention can be demonstrated using standardpharmacological models that are known in the art. Furthermore, it willbe appreciated that the inventive compositions can be incorporated orencapsulated in a suitable polymer matrix or membrane for site-specificdelivery, or can be functionalized with specific targeting agentscapable of effecting site specific delivery. These techniques, as wellas other drug delivery techniques, are well known in the art.

In another embodiment of the invention, the solubility and dissolutionrate of the composition is substantially changed under physiologicalconditions encountered in the intestine, at mucosal surfaces, or in thebloodstream. In another embodiment the solubility and dissolution ratesubstantially decrease the bioavailability of the phenazopyridine,particularly at doses above those intended for therapy.

For each of the described embodiments, one or both of the followingcharacteristics may be realized: The toxicity or side effects associatedwith the phenazopyridine conjugate are substantially lower than that ofphenazopyridine itself. Some of the additional proposed benefits includethe fact that the prodrug is hydrolyzed following oral administration,resulting in increased bioavailability, Tmax increase, increasedpolarity and solubility, and possible active transport by PepT1 or othertransporters. As such the benefits of the prodrug may also providereduced GI exposure to PAP (and commensurate reduction in side effects),a reduced total dose and longer duration of action.

Another embodiment of the present invention provides phenazopyridinecovalently bound to any single amino acid which include the twentynaturally occurring amino acids such as isoleucine, leucine, lysine,methionine, phenylalanine, threonine, tryptophan, valine, alanine,asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline,serine, tyrosine, arginine, or histidine.

In another embodiment, phenazopyridine is covalently bound to adipeptide or a polypeptide.

In another embodiment, phenazopyridine is covalently bound to glycine.

In another embodiment, phenazopyridine is covalently bound to at leastone glycine and an additional amino acid.

In another embodiment, phenazopyridine conjugates of the presentinvention are administered in a therapeutically effective amount to apatient to treat, for example, urinary tract pain, burning, irritation,discomfort, or urgent or frequent urination caused by urinary tractinfections, surgery, injury, or examination procedures, wherein theamount administered to the patient is 90%, 80%, 70%, 60%, 50%, 40%, 30%,20%, 10%, 5%, 1%, or other fractional amount of the standard dose ofunconjugated phenazopyridine that would be administered according tostandard clinical protocols.

In one embodiment, the phenazopyridine conjugates of the presentinvention are administered to a patient and the levels of observed sideeffects such as, for example, nausea, vomiting, and general GI upset,are reduced by 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or morerelative to the levels of side effects observed when a standard dose ofphenazopyridine is administered to a patient.

For each of the recited embodiments, covalent attachment may comprise anamide or carbamate bond.

The abbreviations used herein have their conventional meaning within thechemical and biological arts, unless otherwise specified. For example:“h” or “hr” means hour(s), “min” means minute(s), “sec” means second(s),“d” means day(s), “μL” means microliter(s), “mL” means milliliter(s),“L” means liter(s), “μM” means micromolar, “mM” means millimolar, “M”means molar, “mol” means mole(s), “mmol” means millimole(s), “μg” meansmicrogram(s), “mg” means milligram(s), “×g” means times gravity, “aa”means amino acid(s), “k” means kilo, “μ” means micro, “° C.” meansdegrees Celsius, “THF” means tetrahydrofuran, “DME” meansdimethoxyethane, “DMF” means dimethylformamide, “NMR” means nuclearmagnetic resonance, “BOC” means t-butoxycarbonyl, “psi” refers to poundsper square inch, and “TLC” means thin layer chromatography.

The term “alkyl” as used herein by itself or part of another grouprefers to a straight-chain, branched, or cyclic saturated aliphatichydrocarbon having from one to ten carbons or the number of carbonsdesignated (C₁-C₁₀ means 1 to 10 carbons). Exemplary alkyl groupsinclude methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,isobutyl, tert-butyl, n-pentyl, n-hexyl, isohexyl, n-heptyl,4,4-dimethylpentyl, n-octyl, 2,2,4-trimethylpentyl, nonyl, decyl and thelike.

The term “optionally substituted alkyl” as used herein by itself or partof another group refers to an alkyl as defined above that is optionallysubstituted with one to three substituents independently selected fromnitro, cyano, amino, optionally substituted cycloalkyl, optionallysubstituted heteroaryl, optionally substituted heterocycle, alkoxy,aryloxy, arylalkyloxy, alkylthio, carboxamido, sulfonamido, —COR, —SO₂R,—N(R)COR, —N(R)SO₂R or —N(R)C═N(R)-amino, wherein R may be an alkylgroup. Exemplary substituted alkyl groups include —CH₂OCH₃, —CH₂CH₂NH₂,—CH₂CH₂CN, —CH₂SO₂CH₃ and the like.

The compounds of the present invention may form salts which are alsowithin the scope of this invention. Reference to a compound of thepresent invention herein is understood to include reference to saltsthereof, unless otherwise indicated. The term “salt(s)” as used hereindenotes acidic and/or basic salts formed with inorganic and/or organicacids and bases. In addition, when a compound of the present inventioncontains both a basic moiety and an acidic moiety, zwitterions (“innersalts”) may be formed and are included within the term “salt(s)” as usedherein. Pharmaceutically acceptable (i.e., non-toxic, physiologicallyacceptable) salts are preferred, although other salts are also useful,e.g., in isolation or purification steps which may be employed duringpreparation. Salts of the compounds of the present invention may beformed, for example, by reacting a compound with an amount of acid orbase, such as an equivalent amount, in a medium such as one in which thesalt precipitates or in an aqueous medium followed by lyophilization.

The compounds of the present invention which contain a basic moiety mayform salts with a variety of organic and inorganic acids. Exemplary acidaddition salts include acetates (such as those formed with acetic acidor trihaloacetic acid, for example, trifluoroacetic acid), adipates,alginates, ascorbates, aspartates, benzoates, benzenesulfonates,bisulfates, borates, butyrates, citrates, camphorates,camphorsulfonates, cyclopentanepropionates, digluconates, dodecylsulfates, ethanesulfonates, fumarates, glucoheptanoates,glycerophosphates, hemisulfates, heptanoates, hexanoates, hydrochlorides(formed with hydrochloric acid), hydrobromides (formed with hydrobromicacid), hydroiodides, 2-hydroxyethanesulfonates, lactates, maleates(formed with maleic acid), methanesulfonates (formed withmethanesulfonic acid), 2-naphthalenesulfonates, nicotinates, nitrates,oxalates, pectinates, persulfates, 3-phenylpropionates, phosphates,picrates, pivalates, propionates, salicylates, succinates, sulfates(such as those formed with sulfuric acid), sulfonates (such as thosementioned herein), tartrates, thiocyanates, toluenesulfonates such astosylates, undecanoates, and the like.

The compounds of the present invention which contain an acidic moietymay form salts with a variety of organic and inorganic bases. Exemplarybasic salts include ammonium salts, alkali metal salts such as sodium,lithium, and potassium salts, alkaline earth metal salts such as calciumand magnesium salts, salts with organic bases (for example, organicamines) such as benzathines, dicyclohexylamines, hydrabamines (formedwith N,N-bis(dehydroabietyl)ethylenediamine), N-methyl-D-glucamines,N-methyl-D-glucamides, t-butyl amines, and salts with amino acids suchas arginine, lysine and the like.

The stereochemical terms and conventions used in the specification areconsistent with those described in Pure & Appl. Chem. 68:2193 (1996),unless otherwise indicated.

The term “enantiomeric excess” or “ee” refers to a measure for how muchof one enantiomer is present compared to the other. For a mixture of Rand S enantiomers, the percent enantiomeric excess is defined as|R−S|*100, where R and S are the respective mole or weight fractions ofenantiomers in a mixture such that R+S=1. With knowledge of the opticalrotation of a chiral substance, the percent enantiomeric excess isdefined as ([α]_(obs)/[α]_(max))*100, where [α]_(obs) is the opticalrotation of the mixture of enantiomers and [α]_(max) is the opticalrotation of the pure enantiomer. Determination of enantiomeric excess ispossible using a variety of analytical techniques, including NMRspectroscopy, chiral column chromatography or optical polarimetry.

The terms “enantiomerically pure” or “enantiopure” refer to a sample ofa chiral substance all of whose molecules (within the limits ofdetection) have the same chirality sense.

The terms “enantiomerically enriched” or “enantioenriched” refer to asample of a chiral substance whose enantiomeric ratio is greater than50:50. Enantiomerically enriched compounds may be enantiomerically pure.

The term “asymmetric carbon atom” refers to a carbon atom in a moleculeof an organic compound that is attached to four different atoms orgroups of atoms.

The term “predominantly” means in a ratio greater than 50:50.

The term “leaving group” or “LG” refers to an atom or group that becomesdetached from an atom or group in what is considered to be the residualor main part of the substrate in a specified reaction. In amide couplingreactions, exemplary leaving groups include —F, —Cl, —Br, —OC₆F₅ and thelike.

The term “isolated” for the purposes of the present invention designatesa material (e.g. a chemical compound) that has been removed from itsoriginal environment (the environment in which it is naturally present).

Pharmaceutically acceptable carriers include fillers such assaccharides, for example lactose or sucrose, mannitol or sorbitol,cellulose preparations and/or calcium phosphates, for example tricalciumphosphate or calcium hydrogen phosphate, as well as binders such asstarch paste, using, for example, maize starch, wheat starch, ricestarch, potato starch, gelatin, tragacanth, methyl cellulose,hydroxypropylmethylcellulose, sodium carboxymethylcellulose, and/orpolyvinyl pyrrolidone. If desired, disintegrating agents may be addedsuch as the above-mentioned starches and also carboxymethyl-starch,cross-linked polyvinyl pyrrolidone, agar, or alginic acid or a saltthereof, such as sodium alginate. Auxiliaries are flow-regulating agentsand lubricants, for example, silica, talc, stearic acid or saltsthereof, such as magnesium stearate or calcium stearate, and/orpolyethylene glycol. In one embodiment, dragee cores are provided withsuitable coatings which, if desired, are resistant to gastric juices.For this purpose, concentrated saccharide solutions may be used, whichmay optionally contain gum arabic, talc, polyvinyl pyrrolidone,polyethylene glycol and/or titanium dioxide, lacquer solutions andsuitable organic solvents or solvent mixtures. In order to producecoatings resistant to gastric juices, solutions of suitable cellulosepreparations such as acetylcellulose phthalate orhydroxypropylmethyl-cellulose phthalate, are used. Dye stuffs orpigments may be added to the tablets or dragee coatings, for example,for identification or in order to characterize combinations of activecompound doses.

Other pharmaceutical preparations which can be used orally includepush-fit capsules made of gelatin, as well as soft, sealed capsules madeof gelatin and a plasticizer such as glycerol or sorbitol. The push-fitcapsules can contain the active compounds in the form of granules ornanoparticles which may optionally be mixed with fillers such aslactose, binders such as starches, and/or lubricants such as talc ormagnesium stearate and, optionally, stabilizers. In one embodiment, theactive compound is dissolved or suspended in suitable liquids, such asfatty oils, or liquid paraffin, optionally with stabilizers.

Fatty oils may comprise mono-, di- or triglycerides. Mono-, di- andtriglycerides include those that are derived from C₆, C₈, C₁₀, C₁₂, C₁₄,C₁₆, C₁₈, C₂₀ and C₂₂ acids. Exemplary diglycerides include, inparticular, diolein, dipalmitolein, and mixed caprylin-caprindiglycerides. Preferred triglycerides include vegetable oils, fish oils,animal fats, hydrogenated vegetable oils, partially hydrogenatedvegetable oils, synthetic triglycerides, modified triglycerides,fractionated triglycerides, medium and long-chain triglycerides,structured triglycerides, and mixtures thereof. Exemplary triglyceridesinclude: almond oil; babassu oil; borage oil; blackcurrant seed oil;canola oil; castor oil; coconut oil; corn oil; cottonseed oil; eveningprimrose oil; grapeseed oil; groundnut oil; mustard seed oil; olive oil;palm oil; palm kernel oil; peanut oil; rapeseed oil; safflower oil;sesame oil; shark liver oil; soybean oil; sunflower oil; hydrogenatedcastor oil; hydrogenated coconut oil; hydrogenated palm oil;hydrogenated soybean oil; hydrogenated vegetable oil; hydrogenatedcottonseed and castor oil; partially hydrogenated soybean oil; partiallysoy and cottonseed oil; glyceryl tricaproate; glyceryl tricaprylate;glyceryl tricaprate; glyceryl triundecanoate; glyceryl trilaurate;glyceryl trioleate; glyceryl trilinoleate; glyceryl trilinolenate;glyceryl tricaprylate/caprate; glyceryl tricaprylate/caprate/laurate;glyceryl tricaprylate/caprate/linoleate; and glyceryltricaprylate/caprate/stearate.

Suitable formulations for parenteral administration include aqueoussolutions of the ligand in water-soluble form, for example,water-soluble salts and alkaline solutions. In addition, suspensions ofthe active agent as appropriate oily injection suspensions may beadministered. Suitable lipophilic solvents or vehicles include fattyoils, for example, sesame oil, or synthetic fatty acid esters, forexample, ethyl oleate or triglycerides or polyethylene glycol-400.Aqueous injection suspensions may contain substances which increase theviscosity of the suspension include, for example, sodium carboxymethylcellulose, sorbitol, and/or dextran. Optionally, the suspension may alsocontain stabilizers.

Examples of antioxidants which may be added to the pharmaceuticalcompositions include BHA and BHT.

Pharmaceutical compositions may contain from 0.01% to 99% by weight ofthe active agent. Compositions may be either in single or multiple doseforms. The amount of ligand in any particular pharmaceutical compositionwill depend upon the effective dose, that is, the dose required toelicit the desired gene expression or suppression

Suitable routes of administering the pharmaceutical compositions includeoral, buccal, sublingual, parenteral (including subcutaneous,intramuscular, intravenous, and by naso-gastric tube). It will beunderstood by those skilled in the art that the preferred route ofadministration will depend upon the condition being treated and may varywith factors such as the condition of the recipient. The pharmaceuticalcompositions may be administered one or more times daily.

EXAMPLES OF GENERAL SYNTHETIC METHODS Synthesis ofAminoacyl-phenazopyridine (PAP) Derivatives Example 1 Preparation ofBoc-glycyl-phenazopyridine

To a solution of 875 mg (5 mmol) of Boc-glycine in 15 mL of THF wasadded 955 mg (5 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimidehydrochloride followed by 1.06 g (5 mmol) of phenazopyridine. Thereaction mixture was stirred for 22 h at room temperature at which pointan additional 875 mg (5 mmol) of Boc-glycine and 955 mg (5 mmol) of1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride were added.After stirring for an additional 48 h, the precipitated solid wasfiltered and the filtrate was concentrated to dryness. The residue wasdissolved in 40 mL of ethyl acetate and washed with two 40-mL portionsof saturated aqueous sodium bicarbonate. The organic layer was driedover sodium sulfate, filtered and the filtrate was concentrated underdiminished pressure to give 2.24 g of the crude product as an orangeoil. The product was purified by column chromatography on 62 g of silicagel using 50:50 hexane-ethyl acetate as the eluant.Boc-glycyl-phenazopyridine was obtained as an orange oil: yield 330 mg(18%); ¹H NMR (CDCl₃) δ 1.58 (s, 9H), 4.00 (d, 2H, J=4 Hz), 7.47 (m,4H), 7.80 (m, 2H), 8.17 (d, 1H, J=9 Hz) and 8.29 (br s, 1H). Anal. Calcdfor C₁₈H₂₂N₆O₃.0.25 H₂O: C, 57.67; H, 6.05; N, 22.42. Found: C, 57.86;H, 6.01; N, 22.42.

Example 2 Preparation of Glycyl-phenazopyridine(6-N-Glycylphenazopyridine)

To a solution of 330 mg (0.89 mmol) of Boc-glycyl-phenazopyridine in 20mL of dichloromethane was added 3.10 mL (41.3 mmol) of trifluoroaceticacid. The reaction mixture was stirred at room temperature for 2.5 h atwhich point the reaction was complete. The reaction mixture was pouredinto 40 mL of saturated aqueous sodium bicarbonate solution, the layerswere separated and the organic layer was washed once with 40 mL ofsaturated sodium bicarbonate solution. After drying over sodium sulfate,filtration and removal of the solvent under diminished pressure,glycyl-phenazopyridine was obtained as an orange solid: yield 140 mg(58%); ¹H NMR (CDCl₃) δ 3.5 (s, 2H), 7.4-7.6 (m, 3H), 7.75-7.8 (m, 3H)and 8.2 (d, 1H); mass spectrum (ESI), m/z 271 (M+H)⁺ and 293 (M+Na)⁺.Anal. calcd for C₁₃H₁₄N₆O.0.50 H₂O: C, 55.90; H, 5.41; N, 30.09. Found:C, 56.13; H, 5.16; N, 29.87.

Example 3 Preparation of Glycyl-phenazopyridine Hydrochloride Salt

To a cooled (0−5° C.) solution of 1.0 g (2.70 mmol) ofBoc-glycyl-phenazopyridine in 20 mL of EtOAc was bubbled slowly dry HCl(g) [prepared by adding a 36% solution of HCl (5 mL) to H₂SO₄]. Thereaction mixture was stirred at room temperature for 3 h following whichHPLC analysis showed that the reaction was complete. The thick mixturewas filtered and the product was washed with four 15-mL portions ofEtOAc and dried under diminished pressure over P₂O₅ at 45° C. for 6 h.Glycyl-phenazopyridine dihydrochloride was obtained as an orange solid:yield 878 mg (94%); ¹H NMR (DMSO-d₆) δ 3.88 (s, 2H), 7.51 (m, 4H), 7.89(d, 2H, J=7.2 Hz), 8.09 (d, 1H, J=8.7 Hz), 8.46 (m, 3H) and 11.10 (s,1H). Anal. calcd for C₁₃H₁₆Cl₂N₆O.0.80 H₂O: C, 43.66; H, 4.96; N, 23.50;Cl, 19.83. Found: C, 43.96; H, 4.64; N, 23.60; Cl, 20.10.

Example 4 Preparation of Glycyl-phenazopyridine Mesylate Salt

To a solution of 300 mg (0.8 mmol) of Boc-glycyl-phenazopyridine in 8 mLof dioxane was added dropwise 207 μL (3.2 mmol) of methanesulfonic acid.The reaction mixture was stirred at room temperature for 90 min afterwhich only 4% conversion was observed. After 1 h 45 min, another 414 μL(6.4 mmol) of methanesulfonic acid were added and stirring was continuedat room temperature for 3 h. The precipitated product was filtered,washed with three 6-mL portions of 1,4-dioxane and three 6-mL portionsof acetone and dried under vacuum at 45° C. over P₂O₅ for 18 h.Glycyl-phenazopyridine mesylate salt was obtained as an orange solid:yield 352 mg (94%); ¹H NMR (DMSO-d₆) δ 2.41 (s, 6H), 3.89 (s, 2H),7.43-7.56 (m, 4H), 7.89 (d, 2H, J=7.5 Hz), 8.10 (m, 4H) and 10.87 (s,1H). Anal. calcd for C₁₃H₁₄N₆O.2.65 CH₃SO₃H: C, 35.81; H, 4.72; N,16.01; S, 16.19. Found: C, 35.47; H, 4.79; N, 15.82; S, 15.85.

Example 5 Preparation of Boc-alanyl-phenazopyridine

To a solution of 945 mg (5 mmol) Boc-alanine in 15 mL of THF was added955 mg (5 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimidehydrochloride (EDC) followed by 1.06 g (5 mmol) of phenazopyridine. Thereaction mixture was stirred for 65 h at room temperature at which pointan additional 945 mg (5 mmol) of Boc-alanine and 955 mg (5 mmol) of1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride were added.After stirring for an additional 24 h, the reaction mixture wasconcentrated to dryness, dissolved in 40 mL of ethyl acetate andextracted with two 40-mL portions of saturated aqueous sodiumbicarbonate solution. The organic layer was dried over sodium sulfateand filtered. The filtrate was concentrated under diminished pressure togive 2.1 g of an orange oil. The oil was purified by columnchromatography on 60 g of silica gel using 50:50 hexane-ethyl acetate asthe eluant. Boc-alanyl-phenazopyridine was obtained as an orange oil:yield 610 mg (32%).

Example 6 Preparation of Alanyl-phenazopyridine

To a solution of 610 mg (1.59 mmol) of Boc-alanyl-phenazopyridine in 15mL of dichloromethane was added 5.51 mL (73.6 mmol) of trifluoroaceticacid. The reaction mixture was stirred at room temperature for 3 h atwhich point the reaction was complete. The reaction mixture was pouredinto 40 mL of saturated aqueous sodium bicarbonate solution, the layerswere separated and the organic layer was washed once with 40 mL ofsaturated aqueous sodium bicarbonate. The organic layer was dried oversodium sulfate, filtered and the filtrate was concentrated underdiminished pressure. Alanyl-phenazopyridine was obtained as an orangesolid: yield 290 mg (64%); ¹H NMR (DMSO-d₆) δ 1.3 (d, 3H), 3.6 (q, 1H),7.4-7.7 (m, 4H), 7.9-8.0 (m, 2H) and 8.1 (d, 1H); mass spectrum (ESI),m/z 285 (M+H)⁺ and 307 (M+Na)⁺.

Example 7 Preparation of Boc-methionyl-phenazopyridine

To a solution of 1.24 g (5 mmol) of Boc-methionine in 10 mL of THF wasadded 955 mg (5 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimidehydrochloride (EDC) followed by 1.06 g (5 mmol) of phenazopyridine. Thereaction mixture was stirred at room temperature for 24 h at which pointan additional 1.24 g (5 mmol) of Boc-methionine and 955 mg (5 mmol) of1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride were added.After stirring for an additional 48 h, the reaction mixture wasconcentrated to dryness, dissolved in 40 mL of ethyl acetate andextracted with two 40 mL portions of saturated aqueous sodiumbicarbonate solution. The organic layer was dried over sodium sulfate,filtered and the filtrate was concentrated under diminished pressure.The crude orange oil was purified by column chromatography on 32 g ofsilica gel using 50:50 hexane-ethyl acetate as the eluant.Boc-methionyl-phenazopyridine was obtained as an orange oil: yield 700mg (32%).

Example 8 Preparation of Methionyl-phenazopyridine

To a solution of 700 mg (1.57 mmol) of Boc-methionyl-phenazopyridine in15 mL of dichloromethane was added 2.3 mL (31.4 mmol) of trifluoroaceticacid. The reaction mixture was stirred at room temperature for 2 h atwhich point the reaction was complete. The reaction mixture was pouredinto 60 mL of saturated aqueous sodium bicarbonate solution, the layerswere separated and the organic layer was washed with 40 mL of saturatedaqueous sodium bicarbonate solution. The organic layer was dried oversodium sulfate, filtered and the filtrate was concentrated underdiminished pressure. Methionyl-phenazopyridine was obtained as an orangesolid: yield 247 mg (46%); ¹H NMR (CDCl₃) δ 1.8-1.9 (m, 1H), 2.1 (s,3H), 2.2-2.4 (m, 1H), 2.6-2.8 (m, 2H), 3.7 (m, 1H), 7.4-7.6 (m, 3H),7.8-7.9 (m, 3H) and 8.2 (d, 1H); mass spectrum (ESI), m/z 345 (M+H)⁺ and367 (M+Na)⁺.

Example 9 Preparation of bis-Boc-tryptophanyl-phenazopyridine

To a solution of 2.0 g (5 mmol) of bis-Boc-tryptophan in 15 mL of THFwas added 955 mg (5 mmol) of1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC)followed by 1.06 g (5 mmol) of phenazopyridine. The reaction mixture wasstirred for 6 h at room temperature at which point an additional 2.0 g(5 mmol) of bis-Boc-tryptophan and 955 mg (5 mmol) of1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride were added.After stirring for an additional 72 h, the reaction mixture was filteredand the filtrate was concentrated under diminished pressure. The residuewas dissolved in 40 mL of ethyl acetate and extracted with two 40-mLportions of saturated aqueous sodium bicarbonate. The organic layer wasdried over sodium sulfate, filtered and the filtrate was concentratedunder diminished pressure to give 5.47 g of an orange foam. The crudeproduct was purified by column chromatography on 41 g of silica gelusing 50:50 hexane-ethyl acetate as the eluant.Bis-Boc-tryptophanyl-phenazopyridine was obtained as an orange solid:yield 2.43 g (81%).

Example 10 Preparation of Tryptophanyl-phenazopyridine

To a solution of 360 mg (0.60 mmol) ofbis-Boc-tryptophanyl-phenazopyridine in 15 mL of dichloromethane wasadded 1.80 mL (24.0 mmol) of trifluoroacetic acid. The reaction mixturewas stirred at room temperature for 1.5 h at which point the reactionwas complete. The reaction mixture was poured into 50 mL of saturatedaqueous sodium bicarbonate solution, the layers were separated and theorganic layer was washed once with 40 mL of saturated aqueous sodiumbicarbonate solution. The organic layer was dried over sodium sulfate,filtered and the filtrate was concentrated under diminished pressure.The crude product was purified by chromatography on 41 g of silica gelusing 50:50 hexane-ethyl acetate as eluant. Tryptophanyl-phenazopyridinewas obtained as an orange solid: yield 10 mg (4%); ¹H NMR (CDCl₃) δ3.0-3.2 (m, 1H), 3.4-3.6 (m, 1H), 3.8-4.0 (m, 1H), 7.0-7.3 (m, 4H),7.4-7.6 (m, 4H), 7.8-8.0 (m, 2H), 8.2 (d, 1H) and 10.0 (br s, 1H); massspectrum (ESI) m/z 400 (M+H)⁺ and 422 (M+Na)⁺.

Example 11 Preparation of Boc-valyl-phenazopyridine

To a solution of 1.51 g (7.0 mmol) of Boc-valine in 10 mL of THF wasadded 1.33 g (7.0 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimidehydrochloride (EDC) followed by 1.5 g (7.0 mmol) of phenazopyridine. Thereaction mixture was stirred at room temperature for 24 h at which pointan additional 1.51 g (7.0 mmol) of Boc-valine, 1.33 g (7.0 mmol) of1-(3-dimethylaminopropyl)-3-ethyl carbodiimide hydrochloride and 1.4 g(14 mmol) of N-methylmorpholine were added, and the mixture was stirredfor an additional 24 h. The solvent was concentrated under diminishedpressure and the residue was dissolved in ethyl acetate and washed twotimes with saturated aqueous sodium bicarbonate solution. The organiclayer was dried over sodium sulfate, filtered and the filtrate wasconcentrated under diminished pressure. The crude product was purifiedby column chromatography on silica gel eluting with 1:1 hexanes-ethylacetate to give Boc-valyl-phenazopyridine as an orange oil: yield 300 mg(10%).

Example 12 Preparation of Valyl-phenazopyridine

To a solution of 300 mg (0.73 mmol) of Boc-valyl-phenazopyridine in 10mL of dichloromethane was added 1.72 g (1.1 mL, 14.6 mmol) oftrifluoroacetic acid. The reaction mixture was stirred at roomtemperature for 3.5 h, then was added dropwise to a saturated aqueoussodium bicarbonate solution. The layers were separated and the aqueouslayer was extracted once with dichloromethane. The combined organiclayer was dried over sodium sulfate, filtered and the filtrateconcentrated under diminished pressure. Valyl-phenazopyridine wasobtained as an orange solid: yield 110 mg (48%); ¹H NMR (CDCl₃) δ 0.95(d, 3H), 1.05 (d, 3H), 2.4 (m, 1H), 3.4 (s, 1H), 7.4-7.6 (m, 3H),7.7-7.9 (m, 3H) and 8.1 (d, 1H); mass spectrum (ESI), m/z 313 (M+H)⁺ and335 (M+Na)⁺.

Example 13 Preparation of bis-Boc-lysyl-phenazopyridine

To a solution of 1.73 g (5 mmol) of bis-Boc-lysine in 10 mL of THF wasadded 955 mg (5 mmol) of 1-(3-dimethylaminopropyl)-3-ethyl carbodiimidehydrochloride (EDC) followed by 1.06 g (5 mmol) of phenazopyridine. Thereaction mixture was stirred at room temperature for 24 h. The solventwas removed under diminished pressure and the residue was dissolved inethyl acetate and washed twice with saturated aqueous sodium bicarbonatesolution. The organic layer was dried over sodium sulfate, filtered andthe filtrate was concentrated under diminished pressure to give thecrude product as a red oil. Purification of the crude product on asilica gel column, eluting with 1:1 hexanes-ethyl acetate, gavebis-Boc-lysyl-PAP as an orange oil: yield 360 mg (13%).

Example 14 Preparation of Lysyl-phenazopyridine

To a solution of 360 mg (0.66 mmol) of bis-Boc-lysyl-phenazopyridine in20 mL of dichloromethane was added 3.40 g (2.2 mL, 29.7 mmol) oftrifluoroacetic acid. The reaction mixture was stirred at roomtemperature for 22 h. An additional 1.53 g (13.4 mmol) oftrifluoroacetic acid was added and stirring was continued at roomtemperature for 2 h. The reaction mixture was added to saturated aqueoussodium bicarbonate solution, causing an orange solid to precipitate. Theproduct was filtered, washed twice with heptane and isopropanol, anddried under diminished pressure at room temperature: yield 200 mg (88%);¹H NMR (CD₃OD) δ 1.5-2.2 (m, 6H), 2.9 (t, 2H), 3.7 (t, 1H), 7.5-7.7 (m,4H), 8.0 (m, 2H) and 8.3 (d, 1H); mass spectrum (ESI), m/z 342 (M+H)⁺and 364 (M+Na)⁺.

Example 15 Preparation of Boc-(N-tosyl-histidinyl)-phenazopyridine

A sample of 1.40 g (7.33 mmol) of EDCI was added in one portion to asolution of 3.00 g (7.33 mmol) of Boc-his(Tos)-OH in 60 mL of anhydrousTHF. The reaction mixture was stirred at room temperature for 30 min,then 1.56 g (7.33 mmol) of phenazopyridine was added in one portion. Thereaction mixture was stirred at room temperature for 96 h (until nofurther reaction progress was detected by HPLC). The solvent wasconcentrated under diminished pressure and the residue was dissolved in200 mL of EtOAc, washed successively with 150 mL of water, 150 mL ofsatd. aq. NaHCO₃ solution, 150 mL of brine, and dried (Na₂SO₄). Thesolvent was concentrated under diminished pressure. To remove unreactedphenazopyridine, the oily residue was purified by chromatography on analumina oxide column (elution with CHCl₃, then 99:1 CHCl₃-MeOH). Furtherpurification on a silica gel column (elution with 99:1 CHCl₃-MeOH, then98:2 CHCl₃-MeOH) afforded the product as an orange solid: yield 0.43 g(10%).

Example 16 Preparation of N-Tosyl-histidinyl-phenazopyridine

A sample of 1.28 mL (17.2 mmol) of trifluoroacetic acid was addeddropwise to a solution of 0.26 g (0.43 mmol) ofBoc-(N-tosylhistidinyl)-phenazopyridine in 12 mL of anhydrous CH₂Cl₂.The reaction mixture was stirred at room temperature for 3 h, and thenadded to a saturated aqueous solution of NaHCO₃. The organic layer wasseparated and dried (Na₂SO₄). The solvent was concentrated underdiminished pressure to give the crude product as an orange solid: yield200 mg (100%). A pure sample was obtained using preparative HPLC (93%yield); elution was with 0.1% HOAc in a gradient of CH₃CN; mass spectrum(ESI) m/z 505 (M+H)⁺ and 527 (M+Na)⁺. Anal. calcd for C₂₄H₂₄O₃S.HOAc: C,55.31; H, 5.00; N, 19.85. Found: C, 55.71; H, 4.78; N, 19.57.

Example 17 Preparation of Histidinyl-phenazopyridine

A sample of 65 mg (0.48 mmol) of 1-hydroxybenzotriazole was added to asuspension of 12 mg (0.24 mmol) of N-tosylhistidinyl-phenazopyridine(0.12 g, 0.24 mmol) in 10 mL of anhydrous THF. The reaction mixture wasstirred at room temperature for 2 h before an additional 65 mg (0.48mmol) portion of 1-hydroxybenzotriazole was added and the mixture wasstirred for an additional 3 h. The solvent was concentrated underdiminished pressure and the residue was dissolved in 15 mL of EtOAc andextracted with two 10-mL portions of 0.05 N HCl. The combined aqueouslayer was adjusted to pH˜8 by the addition of a saturated aqueoussolution of Na₂CO₃ and then extracted with three 15-mL portions ofEtOAc. The combined organic layer was dried (Na₂SO₄) and the solvent wasconcentrated under diminished pressure to give an orange solid. It waspurified by preparative HPLC to give the product as a dark orange solid:yield 40 mg (41%); ¹H NMR (500 MHz, DMSO-d₆) δ 1.86 (s, 6H), 3.19-3.31(m, 2H), 4.39 (br s, 1H), 7.46-7.53 (m, 6H), 7.88 (d, 2H), 8.07 (d, 1H),8.45 (br s, 4H) and 9.03 (s, 1H); mass spectrum (ESI) m/z 373 (M+Na⁺);mass spectrum (ESI) m/z 373 (M+Na)⁺.

Synthesis of Phenazopyridine (PAP) Carbamates Example 18 Preparation ofEthylcarbamyl-phenazopyridine

A solution of 4.68 mL (4.68 mmol) of lithium hexamethyldisilazide(LiHMDS) (1M in THF) was added dropwise, over a period of 10 min at roomtemperature, to a solution of 0.50 g (2.34 mmol) of phenazopyridine in10 mL of THF. After an additional 10 min, a solution of 0.26 g (0.23 mL,2.40 mmol) of ethyl chloroformate in 5 mL of THF was added dropwise tothe reaction mixture over a period of 5 min. The reaction mixture wasstirred at room temperature for 1 h. The solvent was concentrated underdiminished pressure and the residue was purified on a silica gel column(17×3 cm). Elution with a stepwise gradient of dichloromethane in hexane(20→80%) gave the monocarbamate as an orange solid: yield 203 mg (30%);¹H NMR (CD₃OD) δ 1.32 (t, 3H, J=7.0 Hz), 4.22 (q, 2H, J=7.0, 14.2 Hz),7.33 (d, 1H, J=9.0 Hz), 7.40 (m, 1H), 7.48 (t, 2H, J=7.2 Hz), 7.82 (d,2H, J=9.9 Hz) and 8.06 (d, 1H, J=9.0 Hz); mass spectrum (ESI) m/z 286(M+H)⁺ and 308 (M+Na)⁺.

Example 19 Preparation of Benzylcarbamyl-phenazopyridine

A solution of 4.68 mL (4.68 mmol) of lithium hexamethyldisilazide(LiHMDS) (1M in THF) was added dropwise, over a period of 10 min at roomtemperature, to a solution of 0.5 g (2.34 mmol) of phenazopyridine in 10mL of THF. After an additional 10 min, a solution of 0.41 g (0.34 mL,2.40 mmol) of benzyl chloroformate in 5 mL of THF was added dropwise tothe reaction mixture over a period of 5 min. The reaction mixture wasstirred at room temperature for 1 h. The solvent was concentrated underdiminished pressure and the residue was purified on a silica gel column(18×3 cm). Elution with a stepwise gradient of dichloromethane in hexane(50→80%), then 1% Et₃N in dichloromethane gave the monocarbamate as anorange solid: yield 273 mg (33%); ¹H NMR (CD₃OD) δ 5.21 (s, 2H),7.32−7.50 (m, 9H), 7.81 (d, 2H, J=9.0 Hz) and 8.06 (d, 1H, J=8.7 Hz);mass spectrum (ESI) m/z 348 (M+H)⁺ and 370 (M+Na⁺)⁺.

Example 20 Preparation of Isobutylcarbamyl-phenazopyridine

A solution of 4.68 mL (4.68 mmol) of lithium hexamethyldisilazide LiHMDS(1M in THF) was added dropwise, over a period of 10 min at roomtemperature, to a solution of 0.5 g (2.34 mmol) of phenazopyridine in 10mL of THF. After an additional 10 min., a solution of 0.32 g (0.31 mL,2.40 mmol) of isobutyl chloroformate in 5 mL of THF was added dropwiseto the reaction mixture over a period of 5 min. The reaction mixture wasstirred at room temperature for 18 h. The solvent was concentrated underdiminished pressure and the residue purified on a silica gel column(17×3 cm). Elution with a stepwise gradient of EtOAc in hexane (0 to15%) gave the bis-carbamate as an orange solid: yield 140 mg (14%),followed by the monocarbamate as an orange solid: yield 202 mg (27%); ¹HNMR (DMSO-d₆) δ 0.93 (d, 6H, J=6.9 Hz), 1.92 (m, 1H), 3.89 (d, 2H, J=6.6Hz), 7.31 (d, 1H, J=8.7 Hz), 7.44 (m, 1H), 7.52 (t, 2H, J=8.7 Hz), 7.86(d, 2H, J=8.1 Hz) and 8.02 (d, 1H, J=8.7 Hz); mass spectrum (ESI) m/z314 (M+H)⁺ and 336 (M+Na)⁺.

Example 21 Preparation of Dodecylcarbamyl-phenazopyridine

A solution of 4.68 mL (4.68 mmol) of lithium hexamethyldisilazide LiHMDS(1M in THF) was added dropwise, over a period of 10 min at roomtemperature, to a solution of 0.5 g (2.34 mmol) of phenazopyridine in 10mL of THF. After an additional 10 min at −5° C., a solution of 0.59 g(0.65 mL, 2.40 mmol) of dodecyl chloroformate in 5 mL of THF (5 mL) wasadded dropwise to the reaction mixture at −5° C. over a period 5 min.The reaction mixture was stirred at −5° C.-0° C. for 1 h and then atroom temperature for 24 h. The solvent was concentrated under diminishedpressure and the residue was purified on a silica gel column (18×3 cm).Elution with 20% EtOAc in hexane gave the slightly impure monocarbamateas an orange solid. The product was dissolved in hot EtOAc (5 mL) andthe mixture was left to cool to room temperature. The precipitatedproduct was collected by filtration and dried under diminished pressure.The phenazopyridine dodecyl monocarbamate was obtained as an orangesolid: yield 361 mg (36%); ¹H NMR (DMSO-d₆) δ 0.83 (t, 3H, J=6.3 Hz),1.22 (m, 18H), 1.6 (m, 2H), 4.09 (t, 2H, J=6.6 Hz), 7.30 (d, 1H, J=8.7Hz), 7.43 (m, 1H), 7.51 (t, 2H, J=7.6 Hz), 7.61 (br s, 2H), 7.85 (d, 2H,J=8.4 Hz), 8.01 (d, 1H, J=8.7 Hz) and 10.08 (s, 1H). Anal. calcd forC₂₄H₃₅N₅O₂.1.25 H₂O: C, 64.33; H, 8.44; N, 15.63. Found: C, 63.96; H,7.83; N, 15.44.

Example 22 Preparation of 2-Ethylhexylcarbamyl-phenazopyridine

A solution of 2.81 mL (2.81 mmol) of lithium hexamethyldisilazide LiHMDS(1M in THF) was added dropwise, over a period of 13 min at −5° C., to acooled solution of 0.3 g (1.40 mmol) of phenazopyridine in 10 mL of THF.After an additional 10 min. at −5° C., a solution of 0.28 g (0.28 mL,1.45 mmol) of 2-ethylhexyl chloroformate in 35 mL of THF was addeddropwise at −5° C. over a period of 5 min. The reaction was stirred at0° C. for 1 h and then at room temperature for 24 h. The solvent wasconcentrated under diminished pressure and the residue was purified bychromatography on a silica gel column (17×3 cm). Elution with a stepwisegradient of EtOAc in heptanes (0→10%) gave the bis-carbamate as anorange syrup: yield 57 mg (7%), followed by the monocarbamate as anorange syrup: yield 309 mg (59%); ¹H NMR (DMSO-d₆) δ 0.86 (m, 6H),1.26-1.40 (m, 8H), 1.56 (m, 1H), 4.01 (d, 2H, J=5.7 Hz), 7.31 (d, 1H,J=8.4 Hz), 7.43 (m, 1H), 7.51 (t, 2H, J=7.5 Hz), 7.85 (d, 2H, J=8.1 Hz),8.01 (d, 1H, J=8.7 Hz) and 10.09 (s, 1H); mass spectrum (ESI) m/z 370(M+H)⁺ and 392 (M+Na)⁺. Anal. calcd for C₂₀H₂₇N₅O₂: C, 65.02; H, 7.37;N, 18.96. Found: C, 65.41; H, 7.43; N, 18.51.

Example 23 Preparation of tert.-Butylcarbamyl-phenazopyridine

A solution of 4.68 mL (4.68 mmol) of lithium hexamethyldisilazide LiHMDS(1M in THF) was added dropwise, over a period of 8 min at 5° C., to asolution of 0.5 g (2.34 mmol) of phenazopyridine in 10 mL of THF. Afteran additional 10 min. at −5° C., a solution of 0.53 g (2.46 mmol) of(Boc)₂O in 5 mL of THF was added dropwise at 0° C. over a period of 10min. The reaction mixture was stirred at 0° C. for 1 h and then at roomtemperature for 2 h. The solvent was concentrated under diminishedpressure and the residue was purified on a silica gel column (18×3 cm).Elution with a stepwise gradient of EtOAc in hexanes (0→10%) gave amixture of the mono and bis-carbamates. The mixture was purified furtheron a preparative HPLC column. The mono carbamate (R_(t) 19.9 min.) wasobtained as an orange foam: yield 451 mg (61%); ¹H NMR (DMSO-d₆) δ 1.60(s, 9H), 7.40 (d, 1H, J=9 Hz), 7.56 (m, 1H), 7.63 (t, 2H, J=7.6 Hz),7.97 (d, 2H, J=8.4 Hz), 8.11 (d, 1H, J=9.0 Hz) and 9.89 (s, 1H); massspectrum (ESI) m/z 314 (M+H)⁺ and 336 (M+Na)⁺. Anal. calcd forC₁₆H₁₉N₅O₂: C, 61.33; H, 6.11; N, 22.35. Found: C, 61.37; H, 6.26; N,22.15. The bis carbamate (R_(t) 22.5 min.) was obtained as an orangesyrup: yield 118 mg (12%); mass spectrum (ESI) m/z 414 (M+H)⁺ and 436(M+Na)⁺.

Example 24 Preparation of Trichloroethylcarbamyl-phenazopyridine

To a solution of 0.50 g (2.34 mmol) of phenazopyridine in 10 mL of THFwas added 0.64 g (4.68 mmol) of oven-dried K₂CO₃ followed by a solutionof 0.5 g (0.32 mL, 2.4 mmol) of trichloroethyl chloroformate in 5 mL ofTHF (added dropwise at room temperature over a period of 20 min.). Thereaction mixture was stirred at room temperature for 4 days. Theinsoluble material was filtered and the solvent was concentrated underdiminished pressure. The residue was purified on a silica gel column(16×3 cm), eluting with a stepwise gradient of EtOAc in hexane (0→8%).The product was obtained as a mixture of mono and bis carbamates. Thismixture was fractionated on a preparative HPLC column. The monocarbamate (R_(t) 20.3 min) was obtained as an orange solid: yield 169 mg(18%); ¹H NMR (DMSO-d₆) δ 4.97 (s, 2H), 7.26 (d, 1H, J=8.4 Hz), 7.44 (m,1H), 7.55 (t, 2H, J=7.5 Hz), 7.63 (brs, 2H), 7.87 (d, 2H, J=8.4 Hz),8.05 (d, 1H, J=9.0 Hz) and 10.69 (s, 1H); mass spectrum (ESI) m/z 390(M+H)⁺ and 413 (M+Na+H)⁺. Anal. calcd for C₁₄H₁₂Cl₃N₅O₂: C, 43.27; H,3.11; N, 18.02; Cl, 27.56. Found: C, 43.50; H, 3.11; N, 17.78; Cl;27.56. The bis carbamate (R_(t) 22.9 min) was obtained as an orangesolid: yield 58 mg (4%); mass spectrum (ESI) m/z 564 (M)⁺.

Example 25 Preparation of n-Butylcarbamyl-phenazopyridine

To a solution of 0.50 g (2.34 mmol) of phenazopyridine in 10 mL of THFwas added 0.64 g (4.68 mmol) of oven-dried K₂CO₃ followed by a solutionof 0.32 g (0.31 mL, 2.4 mmol) of n-butyl chloroformate in 5 mL of THF(added dropwise at room temperature over a period of 10 min). Thereaction mixture was stirred at room temperature for 4 days. Theinsoluble material was filtered and the solvent was concentrated underdiminished pressure. The residue was purified on a short pad of silica,eluting with 20% EtOAc in hexane. The product was purified further on apreparative HPLC column. The mono carbamate (R_(t) 20.1 min) wasobtained as an orange solid: yield 252 mg (34%); ¹H NMR (DMSO-d₆) δ 0.91(t, 3H, J=7.2 Hz), 1.38 (m, 2H), 1.60 (m, 2H), 4.11 (t, 2H, J=5.8 Hz),7.30 (d, 1H, J=8.7 Hz), 7.44 (m, 1H), 7.52 (t, 2H, J=7.2 Hz), 7.86 (d,2H, J=7.2 Hz), 8.02 (d, 1H, J=8.4 Hz) and 10.09 (s, 1H); mass spectrum(ESI) m/z 314 (M+H)⁺ and 336 (M+Na)⁺. Anal. calcd for C₁₆H₁₉N₅O₂: C,61.33; H, 6.11; N, 22.35. Found: C, 61.23; H, 6.11; N, 22.08.

Example 26 Preparation of N^(α)-Boc-glycine Cyanomethyl Ester

To a solution containing 2.0 g (11.4 mmol) of N^(α)-Boc-glycine in 25 mLof EtOAc was added 1.73 g (2.38 mL, 17.1 mmol) of triethylamine followedby 2.05 g (1.19 mL, 17.1 mmol) of bromoacetonitrile. The reactionmixture was stirred at 60° C. under an argon atmosphere for 16 h. Theheterogeneous mixture was cooled to room temperature and filteredthrough a short pad of silica, washing with EtOAc to remove theprecipitated triethylamine hydrobromide. The filtrate was concentratedunder diminished pressure to give N^(α)-Boc-glycine cyanomethyl ester asa colorless syrup which solidified upon standing. The crude product wasused directly in the next step without further purification: yield 2.12g (87%); ¹HNMR (500 MHz, CDCl₃) δ 1.45 (s, 9H), 4.05 (d, 2H, J=5.5 Hz)and 4.79 (s, 2H).

Example 27 Preparation of 6-N-Boc-phenazopyridine and2,6-N,N-bis-Boc-phenazopyridine

To a solution of 3.2 g (15 mmol) of phenazopyridine in 20 mL ofanhydrous THF under argon atmosphere was added 30 mL (30 mmol) of a 1 Msolution of LiHMDS in THF over a period of 15 min. After further 10 min,a solution of 3.27 g (15 mmol) of (Boc)₂O in 15 mL of anhydrous THF wasadded slowly over a period of 20 min and the reaction was allowed toproceed for a further 3 h at room temperature. The solvent wasconcentrated under diminished pressure and the residue was partitionedbetween 100 mL of dichloromethane and 100 mL of 0.1 N aqueous HCl. Theorganic layer was washed with two 50-mL portions of water, dried(Na₂SO₄) and concentrated under diminished pressure. Purification bychromatography on a silica gel column (20×4 cm), eluting withhexanes-ethyl acetate (7:1 and 6:1) gave successively2,6-N,N-bis-Boc-phenazopyridine as an orange foam: yield 1.28 g (20%);silica gel TLC R_(f) 0.44 (5:1 hexanes-ethyl acetate); ¹H NMR (500 MHz,CDCl₃) δ 1.51 (s, 9H), 1.57 (s, 9H), 7.47 (d, 1H, J=7.0 Hz), 7.52 (t,2H, J=7.5 Hz), 7.83 (d, 2H, J=9.5 Hz), 8.15 (t, 2H, J=9.7 Hz) and 10.18(s, 1H); mass spectrum (ESI) m/z 414 (M+H)⁺ and 436 (M+Na)⁺, then amixture of 6-N-Boc-phenazopyridine and 2,6-N,N-bis-Boc-phenazopyridinein 8:1 ratio: yield 1.15 g, and finally 6-N-Boc-phenazopyridine: yield0.99 g. Another 0.61 g of 6-N-Boc-phenazopyridine was recovered from themixture by crystallization from 32 mL of 7:1 hexanes-ethyl acetate.6-N-Boc-phenazopyridine was obtained as an orange solid: yield 1.6 g(34%); silica gel TLC R_(f) 0.34 (5:1 hexanes-ethyl acetate); ¹H NMR(500 MHz, CDCl₃) δ 1.53 (s, 9H), 7.39 (m, 1H), 7.48 (m, 3H), 7.79 (d,2H, J=8.0 Hz) and 8.13 (d, 1H, J=8.5 Hz); mass spectrum (ESI) m/z 314(M+H)⁺ and 336 (M+Na)⁺.

Example 28 Preparation of 2-N-(N^(α)-Boc-glycyl)-6-N-Boc-phenazopyridine

To a solution of 215 mg (0.68 mmol) of 6-N-Boc-phenazopyridine in 9 mLof anhydrous THF was added dropwise 0.69 mL (0.69 mmol) of a 1 Msolution of LiHMDS in THF followed by 147 mg (0.69 mmol) ofN^(α)-Boc-glycine cyanomethyl ester. The reaction mixture was stirred atroom temperature for 45 min. Another 0.69 mL (0.69 mmol) of a 1 Msolution of LiHMDS in THF was added dropwise followed by 147 mg (0.69mmol) of N^(α)-Boc-glycine cyanomethyl ester. This procedure wasrepeated four more times every 45 min. and stirring was continued foranother 19 h at room temperature. The reaction was quenched by slowaddition of 25 mL of water and the reaction mixture was extracted withtwo 25-mL portions of ethyl acetate. The combined organic layer wasdried (Na₂SO₄) and concentrated under diminished pressure. Purificationby chromatography on a silica gel column (15×4 cm) eluting with astepwise gradient of EtOAc in hexanes (10→50%) gave2-N-(N^(α)-Boc-glycyl)-6-N-Boc-phenazopyridine as a brown solid: yield94 mg (29%); ¹H NMR (500 MHz, CDCl₃) δ 1.47 (s, 9H), 1.55 (s, 9H), 4.56(s, 2H), 7.47-7.53 (m, 3H), 7.83-7.88 (m, 2H), 8.17 (d, 11-1, J=9.0 Hz),8.35 (s, 1H) and 10.40 (s, 1H); ¹³C NMR (125 MHz, CDCl₃) δ 47.04, 80.21,81.68, 107.09, 122.71, 129,24, 129.55, 131.29, 133.06, 145.73, 152.12,152.81, 156.22 and 169.71; mass spectrum (ESI) m/z 471 (M+H)⁺ and 493(M+Na)⁺. Anal. calcd for C₂₃H₃₀N₆O₅.1.2 H₂O: C, 56.13; H, 6.64; N,17.08. Found: C, 56.03; H, 6.47; N, 17.02.

Example 29 Preparation of 2-N-Glycyl-phenazopyridine Hydrochloride

To 34 mg (0.07 mmol) of 2-N-(N^(α)-Boc-glycyl)-6-N-Boc-phenazopyridinewas added 2.5 mL (2.5 mmol) of a 1 M solution of HCl in EtOAc. Thereaction mixture was stirred at 65° C. for 2.5 h. Another 2 mL (2 mmol)of 1 M HCl in EtOAc was added and stirring was continued at 65° C. foranother 45 min. The precipitated product was filtered, washed with two5-mL portions of EtOAc and dried under vacuum for 24 h.2-N-Glycyl-phenazopyridine hydrochloride was obtained as a brown solid:yield 20.8 mg (84%); ¹H NMR (DMSO-d₆, 500 MHz) δ 4.16 (d, 2H, J=5.0 Hz),6.49 (d, 1H, J=9.0 Hz), 7.45 (m, 1H), 7.51 (m, 2H), 7.87 (d, 2H, J=9.0Hz), 7.96 (d, 1H, J=9.0 Hz) and 8.30 (br s, NH); ¹³C NMR (DMSO-d₆, 125MHz) δ 42.70, 106.90, 122.88, 128.01, 129.36, 129.66, 130.60, 148.10,152.62, 160.15 and 167.58; mass spectrum (ESI) m/z 271 (M+H)⁺, 272(M+2H)⁺, 293 (M+Na)⁺.

Example 30 Oral Bioavailability of PAP Prodrug in Rats

The oral bioavailability of PAP (phenazopyridine) prodrugs was evaluatedin healthy rats. All the PAP amide (amino acid derivatives) bases weredissolved in 0.1N HCl (the same result can be obtained with a lowermolarity), while the carbamates were dissolved in PEG-400 due to thevery poor aqueous solubility of the PAP-carbamates. The physicochemicalproperties of various PAP derivatives are shown in Table 1. In general,all of the amino acid amide derivatives of PAP had higher watersolubility than those of the PAP-carbamates. In another PK study,PAP.HCl salt, Gly-PAP.HCl salt and Gly-PAP.mesylate salt were dissolvedin water, affording a clear solution in each case prior to oraladministration.

The rats were fasted overnight prior to dosing. Appropriate amount ofeach compound was administered via gastric gavages, and at predeterminedtime (1, 2, 4, 6, and 24 h) blood samples were withdrawn from the rats.The whole blood was centrifuged immediately, and supernatant (plasma)was collected. The plasma samples were assayed for PAP using LC-MS-MS.

TABLE 1 Physicochemical properties of PAP-prodrug and administered oraldose in rats Mol. Solubility in Oral Dose, PAP Compound's Wt. 0.1 N HClmg/kg free-base Generic name (g/mol) (mg/mL) prodrug equivalent PAP ·HCl 249.7 0.5 10.0 8.5 Gly-PAP 270.3 >2 13.4 10.6 Alanyl-PAP 284.3 214.2 10.6 Methionyl-PAP 344.4 1 10.0 6.2 Ethylcarbamyl-PAP 285.3 <0.113.4 10.0 Benzylcarbamyl-PAP 347.4 <0.1 8.2 5.0 Isobutylcarbamyl-PAP313.4 <0.1 7.4 5.0 Histidinyl-PAP 350.4 >10 8.2 5.0 Tryptophanyl-PAP399.0 0.5 9.4 5.0 Valyl-PAP 312.0 >2.5 14.6 10.0 Lysyl-PAP 341.0 >2.516.0 10.0

TABLE 2 Pharmacokinetic analysis of PAP prodrugs following oraladministration in rats PAP-free Actual base Relative Dose equivalentC_(max) T_(max) AUC₀₋₂₄ Bioavailability Compound (mg/kg) (mg/kg) (ng/mL)(h) (ng · h/mL) (%) PAP•HCl 10 8.5 54 <1 182 ± 12 100 Gly-PAP 13.6 10344 <1 2235 ± 132 985 Alanyl-PAP 14.4 10 173 <1 511 ± 41 225Methionyl-PAP 10 5.9 80 <1 193 ± 46 145 Ethylcarbamyl-PAP 13.4 10 BQL ND0 0 Isobutylcarbamyl- 7.4 5 8.6 6 136 ± 25 127 PAP Benzylcarbamyl-PAP8.2 5 8 <1 65 ± 7 61 Histidinyl-PAP 8.2 5 13.7 <1  172 ± 3.4 161Tryptophanyl-PAP 9.4 5 17.1 2  145 ± 4.6 135 Valyl-PAP 14.6 10 213 0.5225 ± 25 105 Lysyl-PAP 16.0 10 249 0.5 821 ± 97 383 AUC: area undercurve of plot plasma concentration vs. time, 0-24 hr RelativeBioavailability (%) = [AUC(prodrug)/AUC(drug) ×Dose(drug)/Dose(prodrug)] 100 BQL: below quantitation limit (<0.5 ng/mL)C_(max): peak plasma concentration T_(max): time to reach peak plasmaconcentration (C_(max))

The pharmacokinetics data is summarized in Table 2. The relativebioavailability of PAP prodrug was in the following order:glycine>lysine>alanine>histidine>methionine>tryptophan>valine>isobutylcarbamyl>benzylcarbamyl>ethylcarbamyl.T_(max) was longer for isobutylcarbamyl-PAP and tryptophanyl-PAP, whilethe T_(max) for the rest of PAP derivatives were less than an hour.

The pharmacokinetics data for various salt forms of Gly-PAP is shown inTable 3. The free base of Gly-PAP, as well as the HCl and mesylatesalts, have significantly enhanced bioavailability as compared with theHCl salt of PAP.

The pharmacokinetics data for various salt forms of Gly-PAP is shown inTable 3. The free base of Gly-PAP, as well as the HCl and mesylatesalts, have significantly enhanced bioavailability as compared with theHCl salt of PAP.

TABLE 3 PAP Pharmacokinetics in rats following oral administration ofPAP•HCl salt, Gly-PAP freebase, Gly-PAP•HCl salt, and Gly-PAP•mesylatesalt Vehicle used to Dose AUC₀₋₆ dissolve (mg/kg, C_(max) (ng · com- PAPbase (ng/ T_(max) h/mL) T_(1/2) Compounds pound equivalent) ml) (h) (SD)(h) PAP•HCl Water 2.5 58 0.25 105 (20) 0.8 Gly-PAP•HCl Water 2.5 140 1.0433 (12) 1.5 Gly- Water 2.5 102 1.0 237 (51) 1.6 PAP•mesylateGly-PAP•free 0.1 N 2.8 211 0.5 378 (57) 1.7 base HCl

Example 31 Alternative Synthesis of2-Amino-6-aminoacetamido-3-E-phenazopyridine Dihydrochloride

Chemical formula: C₁₃H₁₆Cl₂N₆O

Molecular Weight: 343.21

Description of Manufacturing Process depicted in FIG. 16. Gly-PAP is anamide prodrug of phenazopyridine with the carboxyl group of glycinecovalently bound to the nitrogen of the 6-amine of phenazopyridine.

In the first step of the production of Gly-PAP, phenazopyridinehydrochloride (PAP) was converted to the free base using aqueouspotassium carbonate. The free base was extracted into ethyl acetate andisolated by concentration of the solvent in 92% yield. In the secondstep of the process, phenazopyridine free base was treated withBOC-glycine-OSu in DMF using sodium hydride as the base. Theintermediate was isolated by adding water to the reaction mixture whichcaused the product to precipitate. The product was isolated byfiltration, washed with water and recrystallized from isopropyl alcoholto give the intermediate in 34% yield. In the third step BOC-Gly-PAP wasdeprotected by treatment with HCl in ethyl acetate. The product wasisolated in 96% yield by filtration, followed by washing with ethylacetate and drying at 45° C. under vacuum.

Experimental Procedures

Preparation of Phenazopyridine Free Base from the HCl Salt

To a solution of 27.6 grams (200 mmol) of potassium carbonate in 200 mLof water was added 20.0 grams (80 mmol) of phenazopyridine hydrochloridefollowed by 200 mL of ethyl acetate. The mixture was stirred at roomtemperature for 30 minutes. The layers were separated and the aqueouslayer was extracted one time with 100 mL of ethyl acetate. The ethylacetate layer was dried over sodium sulfate, and filtered. The filtratewas concentrated under diminished pressure and the product was driedunder vacuum at room temperature to give an orange solid: yield 15.1grams (92%). NMR (300 MHz, CDCl₃) δ 4.80 (br s, 4H), 6.06 (d, 1H), 7.34(m, 1H), 7.48 (m, 2H), 7.76 (m, 2H), and 7.93 (d, 1H).

Treatment of Phenazopyridine Free Base with N-Boc-Glycine SuccinimideEster

To a suspension of 5.39 g (224.5 mmol) of NaH in 500 mL DMF maintainedat 0-5° C. was added dropwise a solution of 16.0 g (74.40 mmol) ofphenazopyridine in 250 mL of DMF and the reaction was stirred at 0-5° C.for 30 min. N-Boc-glycine succinimide ester (25.4 g, 93.50 mmol) in DMF(190 mL) was added dropwise at 0-5° C. then the mixture was warmed toroom temperature and stirred for 1.5 h. Isopropyl alcohol (25 mL) wasadded dropwise and the mixture was stirred at room temperature for 15min. To the reaction mixture was added 60 grams of Celite™ and it wasstirred for 15 minutes. The reaction mixture was filtered and the filtercake was washed two times with 100 mL of DMF. Water (2,500 mL) was addedto the DMF solution causing an orange solid to precipitate. The mixturewas stirred at room temperature for 30 minutes then the precipitatedproduct was filtered, washed with four 250 mL portion of water and thendried under vacuum over P₂O₅ at 45° C. for 18 h. The crude product wasobtained as an orange powder: yield 12.63 g (46%), purity 95.9% by HPLC.

The crude product (12.63 grams, 34.1 mmol) was dissolved in 170 mL iPrOHat 80° C. to form a clear dark orange solution. It was cooled slowly toroom temperature and then to 0-5° C. The crystallized product wascollected by filtration and dried under vacuum over P₂O₅ at 45° C. for 2hours. The product, BOC-glycine-phenazopyridine, was obtained as a lightorange solid: yield 9.4 g (74%), purity 98.2% by HPLC. Overall yield34%. ¹H NMR (300 MHz, CDCl₃) δ 1.58 (s, 9H), 4.00 (d, 2H, J=4 Hz), 7.47(m, 4H), 7.80 (m, 2H), 8.17 (d, 1H, J=9 Hz), and 8.29 (br s, 1H).

Deprotection of Boc-Glycine-Phenazopyridine to Form Gly-PapDihydrochloride

To a solution of 9.3 grams (25.1 mmol) of BOC-glycine-phenazopyridine in236 mL of ethyl acetate was bubbled HCl gas generated by addingconcentrated HCl (46 mL, 55.2 grams, 1.53 moles) to 133 mL ofconcentrated sulfuric acid in a separate flask. After the addition ofHCl was complete, the reaction mixture was stirred at room temperaturefor 3.5 hours. The solid that was formed was isolated by filtration andwas washed with 500 mL of ethyl acetate. The product was dried underfull vacuum at room temperature to give 8.4 grams of Gly-PAP as anorange solid: yield 98.1%, 98.9% purity by HPLC. ¹H NMR (300 MHz, D₂O) δ3.8 (s, 2H), δ 6.5 (d, 1H), δ 7.3 (br s, 3H), δ 7.6 (br s, 2H), δ 8.0(d, 1H)

Raw Materials and Reagents

Raw Material/ Supplier Reactant Part number (P/N) Purity CAS numberPhenazopyridine Spectrum  >99% 136-40-3 hydrochloride Chemicals P/N:P1059 Boc-glycine-OSu Chem-Impex   99% 3392-07-02 International P/N:03793 Sodium hydride Aldrich   95% 7646-69-7 P/N: 223441 DMFSigma-Aldrich 99.8% 68-12-2 P/N: 227056 Isopropanol EMD Chemicals 99.9%67-63-0 P/N: PX1834-1 HCl (Conc.) Fisher Scientific 37.0% 7647-01-1 P/N:A144-212 Ethyl acetate Fisher Scientific 99.9% 141-78-6 P/N: E195-4H₂SO₄ (Conc.) Fisher Scientific 96.1% 7664-93-9 P/N: A484-212

Example 32 Oral Biovailability of PAP and Gly-PAP (ImprovedBioavailability, Limited Gly-PAP Exposure, Sustained Release of PAP fromGly-PAP, Increased Delivery to Site of Action

Pharmacokinetics for PAP and Gly-PAP (intact prodrug) were assessed inmale rats following administration by oral gavage of mg/kg doses. Ratswere fasted overnight prior to dosing. Blood samples were withdrawn at0.25, 0.5, 1, 2, 4, 6, and 24 hours. The whole blood was centrifugedimmediately, and supernatant (plasma) was collected. The plasma sampleswere assayed for PAP and Gly-PAP by LC-MS-MS.

At a Gly-PAP dose of 4.0 mg/kg (containing 2.5 mg/kg phenazopyridinebase approximating 30 mg of a phenazopyridine HCl human equivalent dose(HED*), an increase of roughly 3-fold was observed for phenazopyridinefrom Gly-PAP compared to the equivalent phenazopyridine hydrochloridedose (2.5 phenazopyridine base content). Plasma levels of Gly-PAP were<5% of those for phenazopyridine from Gly-PAP, illustrating efficienthydrolysis of Gly-PAP with limited systemic exposure to the prodrug.Results are illustrated in FIGS. 1, 3, 4, 11, and 12.

Pharmacokinetics for phenazopyridine for Gly-PAP were determined for alower dose of 0.9 mg/kg Gly-PAP (0.6 mg/kg phenazopyridine base). Whenplotted with concentrations of phenazopyridine from an approximately4-fold higher dose of 2.8 mg/kg phenazopyridine HCl (2.5 mg/kgphenazopyridine base) the lower Gly-PAP dose afforded sustained releaseof phenazopyridine and approximately equal AUC (FIGS. 3 and 12).

When compared to levels of phenazopyridine following oral administrationof 100, 200 and 300 mg in humans (approximate human equivalent dose(HED) based on 60 kg person (6.2 rat conversion factor)—Guidance forIndustry: Estimating the Maximum Safe Starting Dose for Initial ClinicalTrials for Therapeutics in Adult Healthy Volunteers), the levels ofphenazopyridine where considerably higher in rats at HEDs ofapproximately 100 mg or less for both Gly-PAP and phenazopyridinehydrochloride. Although the absolute bioavailability of phenazopyridinehydrochloride in humans has not been determined it appears to be poorlyabsorbed. (Shang E, et al. Determination of phenazopyridine in humanplasma via LC-MS and subsequent development of a pharmacokinetic model.Anal Bioanal Chem. 2005 May; 382(1):216-22). Rat pharmacokinetics havebeen found to be highly correlated with human pharmacokinetics. (SeeChiou, W. L, et al., Pharm. Res. 17:135-140 (2000); Chiou, W. L., etal., Pharm. Res. 15:1474-1479 (1998); and Chiou, W. L., et al., J. Clin.Pharmacol. Ther. 38:532-539 (2000).

Pharmacokinetics for PAP and Gly-PAP (intact prodrug) were assessed indogs following administration by oral gavage of mg/kg doses. Blood(approximately 2 mL) was collected from a jugular vein into tubescontaining lithium heparin anticoagulant predose and at 0.083, 0.25,0.5, 1, 2, 4, 8, 12, and 24 hours postdose. Urine was collected intoplastic containers surrounded by wet ice predose (−18 to 0) and 0 to 24hours postdose. The volume of each sample was recorded. Plasma and urinesamples were assayed for PAP and Gly-PAP by LC-MS-MS.

In dogs Gly-PAP afforded effective delivery of phenazopyridine followingoral administration of 8.1 mg/kg Gly-PAP, approximating a HED(Approximate human equivalent dose (HED) based on 60 kg person (1.8 dogconversion factor—Guidance for Industry: Estimating the Maximum SafeStarting Dose for Initial Clinical Trials for Therapeutics in AdultHealthy Volunteers) of 200 mg of phenazopyridine HCl. Phenazopyridinefrom phenazopyridine HCl containing an equivalent amount ofphenazopyridine resulted in greater plasma bioavailability ofphenazopyridine; however, a greater amount of phenazopyridine wasdelivered to the urine from Gly-PAP. The site of action forphenazopyridine is the bladder and urethra. Plasma T_(max) was increasedfor phenazopyridine from Gly-PAP as compared to phenazopyridine fromphenazopyridine HCl, illustrating sustained release. Exposure (AUC₀₋₂₄)to Gly-PAP was less than 10% of that for phenazopyridine in dogsfollowing administration of Gly-PAP (FIGS. 13-15).

The pharmacokinetics of various salts of Gly-PAP were compared followingoral administration to rats. All salt forms improved the oralbioavailability of phenazopyridine as compared to bioavailability fromphenazopyridine HCl. Gly-PAP HCl afforded the highest bioavailability(FIG. 17).

Example 33 Reduced Emesis in Dogs

Dogs (1 male/1 female) were dosed by oral gavage 3 times (TID), onceevery 8 hours, with 40 mg/kg Gly-PAP or 29 mg/kg phenazopyridine HCl(doses contained an equivalent amount of 24.8 mg/kg phenazopyridinebase). A single observation of vomitus was observed for Gly-PAP comparedto four observations of vomitus for phenazopyridine HCl. Results showingreduction of the GI side effect of emesis are illustrated in FIG. 18.

Having now fully described this invention, it will be understood bythose of ordinary skill in the art that the same can be performed withina wide and equivalent range of conditions, formulations and otherparameters without affecting the scope of the invention or anyembodiment thereof. All patents, patent applications and publicationscited herein are fully incorporated by reference herein in theirentirety.

1. A compound of Formula I:

wherein, R₁ and R₂ are independently (a) hydrogen; (b) the residue of anamino acid or peptide; (c)

wherein R₃ is an optionally substituted alkyl or arylalkyl; or (d) theresidue of an amino acid wherein the amine of the amino acid isprotected with a t-butylcarbonyl; wherein at least one of R₁ and R₂ isother than hydrogen.
 2. The compound of claim 1, wherein R₁ is an aminoacid residue and R₂ is hydrogen.
 3. The compound of claim 1, wherein R₁is an (L-) amino acid residue and R₂ is hydrogen.
 4. The compound ofclaim 2, wherein the amino acid residue is selected from the groupconsisting of the residues of alanine, arginine, asparagine, asparticacid, cysteine, glycine, glutamic acid, glutamine, histidine,isoleucine, leucine, lysine, methionine, proline, phenylalanine, serine,tryptophan, threonine, tyrosine, and valine.
 5. The compound of claim 3,wherein the (L-) amino acid residue is selected from the groupconsisting of the residues of alanine, arginine, asparagine, asparticacid, cysteine, glutamic acid, glutamine, histidine, isoleucine,leucine, lysine, methionine, proline, phenylalanine, serine, tryptophan,threonine, tyrosine, and valine.
 6. The compound of claim 1, wherein R₁is the amino acid residue of glycine and R₂ is hydrogen.
 7. The compoundof claim 1, wherein R₁ is the amino acid residue of lysine and R₂ ishydrogen.
 8. The compound of claim 1, wherein R₁ is the amino acidresidue of alanine and R₂ is hydrogen.
 9. The compound of claim 1,wherein R₁ is (c), R₃ is selected from the group consisting of ethyl,benzyl, isobutyl, dodecyl, ethylhexyl, trichloroethyl, and n-butyl, andR₂ is hydrogen.
 10. The compound of claim 1, wherein R₂ is an amino acidresidue and R₁ is hydrogen.
 11. The compound of claim 1, wherein R₂ isan (L-) amino acid residue and R₁ is hydrogen.
 12. The compound of claim10, wherein the amino acid residue is selected from the group consistingof the residues of alanine, arginine, asparagine, aspartic acid,cysteine, glycine, glutamic acid, glutamine, histidine, isoleucine,leucine, lysine, methionine, proline, phenylalanine, serine, tryptophan,threonine, tyrosine, and valine.
 13. The compound of claim 11, whereinthe (L-) amino acid residue is selected from the group consisting of theresidues of alanine, arginine, asparagine, aspartic acid, cysteine,glutamic acid, glutamine, histidine, isoleucine, leucine, lysine,methionine, proline, phenylalanine, serine, tryptophan, threonine,tyrosine, and valine.
 14. The compound of claim 1, wherein R₂ is theamino acid residue of glycine and R₁ is hydrogen.
 15. The compound ofclaim 1, wherein R₂ is the amino acid residue of lysine and R₁ ishydrogen.
 16. The compound of claim 1, wherein R₂ is the amino acidresidue of alanine and R₁ is hydrogen.
 17. The compound of claim 1,wherein R₂ is (c), R₃ is selected from the group consisting of ethyl,benzyl, isobutyl, dodecyl, ethylhexyl, trichloroethyl, and n-butyl, andR₂ is hydrogen.
 18. A pharmaceutical composition comprising atherapeutically effective amount of the compound of claim
 1. 19. Thepharmaceutical composition of claim 18, wherein the therapeuticallyeffective amount of the compound is less than 50% of the therapeuticallyeffective amount of an unconjugated phenazopyridine.
 20. A method oftreating an individual comprising administering a therapeuticallyeffective amount of the compound of claim
 1. 21. The method of claim 20,wherein the therapeutically effective amount of the compound is lessthan 50% of the therapeutically effective amount of an unconjugatedphenazopyridine.
 22. The method of claim 20 for the treatment of urinarytract pain, burning, irritation, discomfort, or urgent or frequenturination caused by urinary tract infections, surgery, injury, orexamination procedures.
 23. The method of claim 20, wherein the sideeffects of the administration of the compound are less severe than theside effects of the administration of unconjugated phenazopyridine.